Operating Segments and Related Disclosures - Selected Financial Information for Each Reportable Segment (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Net Sales:
Net sales	$ 96.3	$ 528.2	$ 484.1	$ 459.6	$ 405.3	$ 532.2	$ 463.8	$ 408.4	$ 356.9	$ 1,877.2	$ 1,761.3	$ 1,708.3
Reconciliation of segment performance to loss from continuing operations before income taxes:
Interest expense	(3.8)									(30.9)	(32.5)	(50.4)
Interest income	0.0									3.5	0.6	0.3
Stock-based compensation expense	0.4									(22.0)	(12.9)	(8.6)
Loss from continuing operations before income taxes	9.0									86.9	29.3	(16.8)
Capital Expenditures	1.2									29.4	47.6	36.8
Depreciation and amortization	5.1									72.6	64.9	65.1
Pension Benefits
Reconciliation of segment performance to loss from continuing operations before income taxes:
Contributions by employer, recoverable in current year government contracts										33.7	27.5
Aerospace and Defense
Reconciliation of segment performance to loss from continuing operations before income taxes:
Capital Expenditures	1.2									29.3	46.4	36.8
Depreciation and amortization	5.0									71.6	64.2	64.4
Real Estate
Reconciliation of segment performance to loss from continuing operations before income taxes:
Capital Expenditures	0.0									0.0	0.0	0.0
Depreciation and amortization	0.1									0.7	0.6	0.7
Operating Segments
Net Sales:
Net sales	96.3									1,877.2	1,761.3	1,708.3
Segment Performance:
Segment performance	15.4									180.4	147.6	83.3
Reconciliation of segment performance to loss from continuing operations before income taxes:
Segment performance	15.4									180.4	147.6	83.3
Operating Segments | Aerospace and Defense
Net Sales:
Net sales	95.8									1,870.8	1,753.9	1,660.0
Segment Performance:
Aerospace and Defense	19.6									202.9	184.1	165.7
Environmental remediation provision adjustments	0.1									(7.5)	(18.3)	(16.6)
Retirement benefits, net	(4.1)									(19.5)	(22.5)	(50.2)
Unusual items	(0.4)									2.0	0.0	(50.0)
Segment performance	15.2									177.9	143.3	48.9
Reconciliation of segment performance to loss from continuing operations before income taxes:
Segment performance	15.2									177.9	143.3	48.9
Unusual items	(0.4)									2.0	0.0	(50.0)
Operating Segments | Real Estate
Net Sales:
Net sales	0.5									6.4	7.4	48.3
Segment Performance:
Segment performance	0.2									2.5	4.3	34.4
Reconciliation of segment performance to loss from continuing operations before income taxes:
Segment performance	0.2									2.5	4.3	34.4
Segment Reconciling Items
Segment Performance:
Unusual items	0.0									(1.0)	(34.5)	(1.9)
Reconciliation of segment performance to loss from continuing operations before income taxes:
Interest expense	(3.8)									(30.9)	(32.5)	(50.4)
Interest income	0.0									3.5	0.6	0.3
Stock-based compensation expense	0.4									(22.0)	(12.9)	(8.6)
Unusual items	0.0									(1.0)	(34.5)	(1.9)
Corporate
Segment Performance:
Retirement benefits, net	(1.5)									(20.0)	(18.9)	(17.4)
Reconciliation of segment performance to loss from continuing operations before income taxes:
Corporate and other	(1.5)									(23.1)	(20.1)	(22.1)
Capital Expenditures	0.0									0.1	1.2	0.0
Depreciation and amortization	$ 0.0									$ 0.3	$ 0.1	$ 0.0